fst

This crate provides a fast implementation of ordered sets and maps using finite
state machines. In particular, it makes use of finite state transducers to map
keys to values as the machine is executed. Using finite state machines as data
structures enables us to store keys in a compact format that is also easily
searchable. For example, this crate leverages memory maps to make range queries
very fast.

Check out my blog post
Index 1,600,000,000 Keys with Automata and
Rust
for extensive background, examples and experiments.

Dual-licensed under MIT or the UNLICENSE.

Documentation

https://docs.rs/fst

The
regex-automata
crate provides implementations of the fst::Automata trait when its
transducer feature is enabled. This permits using DFAs compiled by
regex-automata to search finite state transducers produced by this crate.

Installation

Simply add a corresponding entry to your Cargo.toml dependency list:

[dependencies]
fst = "0.4"

Example

This example demonstrates building a set in memory and executing a fuzzy query
against it. You’ll need fst = "0.4" with the levenshtein feature enabled in
your Cargo.toml.

use fst::{IntoStreamer, Set};
use fst::automaton::Levenshtein;

fn main() -> Result<(), Box<dyn std::error::Error>> {
  // A convenient way to create sets in memory.
  let keys = vec!["fa", "fo", "fob", "focus", "foo", "food", "foul"];
  let set = Set::from_iter(keys)?;

  // Build our fuzzy query.
  let lev = Levenshtein::new("foo", 1)?;

  // Apply our fuzzy query to the set we built.
  let stream = set.search(lev).into_stream();

  let keys = stream.into_strs()?;
  assert_eq!(keys, vec!["fo", "fob", "foo", "food"]);
  Ok(())
}

Check out the documentation for a lot more examples!

Cargo features

• levenshtein - Disabled by default. This adds the Levenshtein
  automaton to the automaton sub-module. This includes an additional
  dependency on utf8-ranges.